Natural gas is a vital component of the world's energy supply. It is a major source of electricity generation, is a relatively clean automobile fuel, and is used in residential homes for cooking, heating and cooling. Natural gas is a combustible mixture of hydrocarbon gases formed primarily of methane, which in its pure form is colorless and odorless. It is found in reservoirs underneath the earth, often associated with oil deposits. The United States has vast resources of natural gas available for extraction, but until recent technological advances, the ability to access these resources was limited.
Hydraulic fracturing is a technique used to facilitate natural gas and oil recovery. It was first used commercially by Halliburton in 1949, but it did not become widely adopted until resent technological improvements rendered it more effective and cost-efficient. It is now used worldwide in tens of thousands of oil and natural gas wells. Fracturing permits gas recovery from unconventional reservoirs such as shale rock and coal beds, which may not otherwise be sufficiently porous and permeable to allow gas to flow from the rock into the wellbore at economically feasible rates. The process creates fractures in underground rock formations as highly pressurized hydraulic fracturing fluid is injected into the reservoir to force tiny cracks in the rock to release gas trapped inside. A typical horizontal well (such as those drilled for the Barnett, Marcellus or Haynesville Shales) uses 3 to 5 million gallons of fracturing fluid. Hydraulic fracturing fluid is comprised of 99.5% water and proppant. Proppant is a material that prevents fractures from closing when the injection is stopped; the material is usually grains of sand or ceramic. In addition to water and proppant, the fracturing fluid may contain hundreds of other chemical additives.
When extracting natural gas and other fluids from horizontal shale production formations, it is extremely valuable for the producer to know which portion of the formation, and which portion of the horizontal production pipe, is producing the natural gas (“flow measurement”).
Furthermore, considerable controversy surrounds the environmental and health effects of natural gas extraction. Gas drilling can potentially result in contamination of groundwater, air pollution, and public exposure to natural gas and toxic chemicals. Groundwater contamination from oil and gas leaks has been identified as one of the most significant environmental threats facing the United States (“leakage detection”).
Therefore, it would be a significant advancement in the state of the art to provide a system that addresses both the flow measurement problem and the leakage detection problem. Therefore, the present inventors have developed a system, method, and apparatus for monitoring groundwater, rock, and casing for production flow and leakage of hydrocarbon fluids.
It is against this background that the present invention was developed.